Well, they actually DID find a cure for the RCI, now, didn't they? TWO cures, in fact. One individual cure from Mother Winter, and one global cure from the Red King's own hand.
Yes, they were well beyond the reach of a mortal practitioner, or the assembled resources of the Fellowship, and one was beyond the thought processes, at the least, of the assembled Council. But they were available.
They are demonstrable evidence that the desired effect is, in theory, possible, and both canonical instances of a 'cure' were on scale far surpassing the proposed 'exorcism', the first being a solution to ANY 'enchantment', and the second being GLOBAL.
First of all, note that the Red King thing was a death spell of mythic size, not a cure of vampirism
and that in the DFRPG reality, the Winter Mother is only one rung below The Almighty on the six rung "Supernatural Heavyweights" table (OW28) that doesn't even mention the most powerful members of the White Council.
The fact that some entity, somewhere in the DF reality, can accomplish something says nothing about the the capabilities of other non-similar entities. If you take your logic (Mother Winter can accomplish a thing, therefore a Wizard could eventually learn to accomplish the same thing through mortal magic) to the extreme, then you'd have to conclude that Harry is, in fact capable of Creating all of Existence, if only he tagged enough Aspects (The Almighty can accomplish a thing, therefore a Wizard could learn to accomplish the same thing through mortal magic).
In any case, the question isn't "Can a Red Court Infection be removed", it's "What would an exorcism do to a White Court Vampire". And while the question is certainly a matter of opinion and may be approached differently in different gaming groups, I stand by my opinion that DFRPG vampirism is a curse/infection/inherited condition rather than a possession, and that therefore no exorcism will have any effect on any member of any of the three Courts. Note that I similarly feel that an exorcism would have no effect on someone suffering from a birth defect or even from the common cold (though your typical drug store can sell you something that might help a bit with the latter).